Voltage regulator with continuously variable dc reference



United States Patent US. Cl. 32322 16 Claims ABSTRACT OF THE DISCLOSUREA monolithic voltage regulator having a high current capability, aconstant low output impedance from DC to several hundred kilocycles, anda high ripple reduction factor. The regulator has excellent transientresponse; it provides a wide range of regulated output voltage and has alow temperature drift. The voltage regulator includes an inputdifferential amplifier stage having a pair of transistors coupled to acurrent sink (a current source passing current to ground), and one ofthe transistors in the pair is connected through a current gain stage toan output terminal. A DC reference shifting circuit is connected to theinput of one transistor in the pair and provides a reference voltage tothe differential amplifier stage which has been translated to providethe required voltage level at the output terminal. The output terminalis connected directly to the input of the other transistor in the pairin order to achieve a unity feedback factor to provide excellentconstant loop performance independent of the output voltage. The directcoupled feedback connection eliminates any undesirable gain loss andphase shifting due to resistance in the input circuits of thedifferentially coupled transistor pair.

BACKGROUND OF THE INVENTION This invention relates generally to voltageregulators and more particularly to a monolithic series voltageregulator featuring improved AC and DC performance.

One conventional approach to series voltage regulation involves feedingthe output voltage of the regulator back through a resistive dividerfeedback network to a differential amplifier stage thereof to providethe necessary DC voltage gain to achieve the required DC output voltagefrom a fixed, temperature-compensated reference voltage. A conventionalprior art circuit using this approach is shown in FIG. 1 of the drawingsand will be described further below in the detailed description of theinvention.

This type of conventional prior art circuit and including variousmodifications thereof has several operational disadvantages, one ofwhich being that the closed loop gain is dependent upon the outputvoltage. This output voltage dependence changes the feedback factor ofthe regulator circuit and degrades the closed loop performance thereof.

Another disadvantage of the prior art circuit in FIG. 1 is that theresistors which are connected in the input circuits of the differentialamplifier stage cause a loss of gain of the stage, and further thisresistance in combination with unavoidable capacitance produces a phaselag in the loop transmission (loop gain) which degrades the stabilityand frequency response thereof.

Another disadvantage of the circuit in FIG. 1 is that the resistorswhich are connected in the base circuits of the transistors of thedifferential amplifier stage produce undesirable DC voltage drops as aresult of base current flow therein. These base resistors require amatch in the current gain of the transistors and limit the maximumcollector bias currents which can be used in the stage.

"ice

A further disadvantage of the conventional prior art circuit in FIG. 1is that a pole-splitting capacitor (not shown) is usually connectedbetween electrodes of one of the transistors in the differentialamplifier stage. This pole-splitting capacitor causes a loss offrequency response Within the amplifier and, in combination withadditional load capcitance connected to the output of the voltageregulator, can cause the regulator to become unstable and provideundesired oscillations in the output waveform.

SUMMARY OF THE INVENTION The present invention has been constructed toovercome all of the above-described disadvantages of the prior artcircuit in FIG. 1 and includes as one objective thereof the provision ofa new and improved monolithic series voltage regulator having bothexcellent DC temperature stability and improved AC performance.

Another object of this invention is to provide a monolithic seriesvoltage regulator having a constant low output impedance from DC toseveral hundred kilocycles.

Another object of this invention is to provide a voltage regulatorhaving a high ripple reduction factor and an excellent transientresponse for abrupt changes in load current.

A further object of this invention is to provide a voltage regulatoroperative over a wide range of output voltages and having a very lowtemperature drift of the output voltage.

The present invention features a monolithic series voltage regulatorhaving a wideband feedback loop requiring capacitive compensation onlyat the output node of the regulator.

Another feature of this invention is the provision of a separateinternal voltage regulator to supply a variable reference voltage to themain regulator.

Another feature of this invention is the provision of a series voltageregulator operating with unity closed-loop gain and having no inputresistance connected to the control differential amplifier stagethereof. The elimination of this input resistance results in increasedloop gain, improved frequency response and eliminates biasing and DCdrift problems due to input base current in the differential amplifierstage. Therefore, the performance of the regulator is independent of theoutput voltage setting used.

Another feature of this invention is a DC reference shifting circuitwhich provides a reference voltage for the main regulator and maintainsthis voltage at a substantially constnt value independent oftemperature. The low value input base currents to the differentialamplifier portion of this reference shifting circuit allows an externalresistor divider feedback network to be used to achieve the desiredoutput voltage reference. This reference shifting circuit does notrequire an exact base resistance match at the input of the differentialamplifier portion thereof.

Another feature of the present invention is the provision of trackingbetween PNP transistors forming constant current sources for thecollectors of the differential amplifiers in the regulator and the NPNcurrent sinks which are connected to the emitters of these amplifiers.This current sink-current source tracking arrangement prevents thedifferential amplifiers from degrading the temperature stability of theoverall regulator circuit as a result of unequal bias current changes.

Another feature of this invention is a provision of a control amplifierstage including a Darlington output current gain stage connected to apair of differentially coupled transistors. The DC bias current of theunloaded collector of a transistor in the differential amplifier stageis used to prebias the input transistor of the Darlington stage. Thisbiasing arrangement insures that this input transistor will alwaysconduct a minimum current, i.e.,

3 guarantee transistor current gain of this transistor even for very lowvalues of load current.

Another feature of this invention is a provision of bias circuitry toprovide a basic reference voltage with a zero temperature coefficientwhich is derived from a Zener diode with a positive temperaturecoeflicient. This bias circuitry also provides a reference current witha zero temperature coefficient. This reference current is used to biasboth the PNP current sources and the NPN current sinks in such a mannerthat both these current sources and sinks also have a zero temperaturecoefficient and also track in magnitude.

Another feature of this invention is a provision of a starting andshut-down circuit which can be externally electrically controlled tocause the complete regulator to enter a shut-down or standby mode ofoperation. When shut-down, the DC bias current drain of the completeregulator will drop to a very low value and the output voltage will fallto zero volts.

Another feature of this invention is the inclusion of a lateral PNPdevice connected as a high voltage diode to prevent the discharge to themonolithic regulator circuit of the energy which may be stored on anexternally connected noise filter capacitor.

Another feature of this invention is a provision of an internalregulator circuit which is easily made to pass only low frequencies bythe use of a relatively small valued external capacitor. This bandlimiting is used to reduce the RMS value of the noise which originateswithin the Zener diode and would otherwise appear at the output of theregulator.

In the drawings:

FIG. 1 is a schematic diagram of one conventional prior art circuitwhich will be described in order that the circuit of this invention maybe better understood;

FIG. 2 is a schematic diagram of the main control amplifier portion ofthe series voltage regulator according to the present invention;

FIG. 3 is a DC reference shifting circuit which is connected between apoint of basic zero temperature coeflicient reference voltage, VR, andthe main control amplifier of FIG. 2;

FIG. 4 is a block diagram illustration of the complete series voltageregulator of the present invention; and

FIG. 5 is a schematic diagram of the series voltage regulator embodyingthis invention.

DESCRIPTION OF THE INVENTION Briefly described, the present invention isdirected to a series voltage regulator having a main control amplifierportion including a differential transistor pair which is connected to acurrent sink. A Darlington current gain output stage is connectedbetween one of the transistors in the differential pair and a circuitoutput terminal, and the other of the transistors'in the pair isconnected to an intermediate point in the Darlington stage to insuretransistor current gain at low values of load current. A DC referenceshifting circuit is connected between a reference voltage and the onetransistor in the differential pair to provide a desired temperaturestabilized DC reference potential for the main control amplifier whichis equal to the desired output voltage. The input of the othertransistor in the differential pair is connected directly to the outputterminal of the regulator so that 100% of the output voltage is fed backto the differential pair, resulting in excellent AC performance of theregulator.

Referring in detail to FIG. 1, there is shown a conventional prior artseries voltage regulator circuit including a pair of emitter-coupledtransistors and 12 connected to a current sink 9. A current gain stage'33 is connected to transistors 10 and 12 and includes transistors 14and 16 therein which are connected in a Darlington connection. A zerotemperature coefiicient reference voltage device 13 including forwardand Zener diodes and 17 respectively, is connected in series with asource of constant current 23 between an input voltage terminal 27 and apoint of reference or ground potential 8. A resistive divider network,including resistors 19 and 21, is connected between the voltage outputterminal 29 and a point of reference potential 8, and an intermediatepoint between resistors 19 and 21 is connected to the base of transistor12. A base resistor 11 is connected between the voltage reference device13 and the base of transistor 10 to provide a balancing resistance atthe base of transistor 10 (equal to the impedance seen by the base of12) and thus to provide a symmetrical circuit. Transistors 10 and 12conduct current in the half to one milliamp range and this current ismultiplied by the betas, i.e., current gains, of transistors 14 and 16to provide an output load current in the hundred milliampere range.

In operation, a fraction of the voltage at the output terminal 29 issampled at the base of transistor 12. If this potential rises higherthan the reference voltage applied to transistor 10, transistor 12 willbecome more conductive than transistor 10 and divert more current fromthe current source 25 into the collector of 12. Such current diversionaway from the base of transistor 14 reduces the output current and thusreduces the output voltage. This action stabilizes the voltage level atthe output terminal 29 at a predetermined value. Conversely, when thevoltage at the output terminal 29 swings lower than this value,transistor 10 will become more conductive than transistor 12 and thusmore current from the current source 25 will begin to flow into thecurrent gain stage 33, in creasing the available load current andpulling up the output voltage.

The disadvantages of the prior art circuit in FIG. 1 have been set forthabove in some detail but will be restated here with reference to theconnections and components in the circuit in FIG. 1. One disadvantage ofthe circuit in FIG. 1 is that the voltage divider formed by resistors 19and 21 causes the loop gain (or loop trans mission) to change as theoutput voltage at terminal 29 changes. Accordingly, there is not aconstant loop performance in FIG. 1 independent of the output voltage.

Another disadvantage of the circuit in FIG. 1 is that input"capacitance, which appears at the bases of transistors 10 and 12,introduces phase lag in the loop which tends to make the circuitunstable. Additionally, the resistance at the base of transistors 10 and12 will require matched current gains of these transistors, will limitthe maximum base current allowed, and will require matched temperaturecoefiicients of resistance.

With the above disadvantages of the circuit of FIG. 1 in mind, the novelcircuit according to the present invention will now be described. InFIG. 2 first and second emittercoupled transistors 20 and 22 areconnected to a current sink 9 and are further connected as shown to theDarlington current gain stage 31. Stage 31 includes transistors 24 and26 which are connected emitter-to-base in the well known Darlingtonmanner. The collector of transistor 20 is tied to the base of transistor26 and to the emitter of transistor 24 to insure that the transistor 24always conducts a minimum current to guarantee current gain of thisdevice for small values of load current.

The base of the second emitter-coupled transistor 22 is tied directly tothe output terminal 33 so that of the output voltage is fed-back totransistor 22 and enables the circuit to operate with a feedback factorof one. This large amount of feedback results in excellent ACperformance of the circuit. Resistors are not required at the bases oftransistors 20 and 22, and the above-described disadvantages associatedwith these resistors are therefore not present.

The second emitter-coupled transistor 22 Samples the output voltage, andcompares it with the reference voltage at the base of transistor 20. Theoutput voltage is compared with the reference voltage in such a manneras to compensate for changes in the output voltage due to variations inthe load current. The Darlington current gain stage 31 is connected in amanner somewhat similar to the current gain stage 33 in FIG. 1 and acurrent source 25 is connected to the collector of emitter-coupledtransistor 22 and to the base of transistor 24. Current will dividebetween transistors 22 and 4 during the sample and compare operation.The current source 25 will supply a current of 1/2 where I is the totalcurrent through sink 9.

The reference voltage applied to terminal 20 is provided by a DCreference shifting circuit which is similar to the circuit in FIG. 1 andis illustrated in FIG. 3. Since the circuit of FIG. 1 can be modified byintroducing the unbiased Darlington connection shown in FIG. 3,excellent DC characteristics can be obtained. It is worth noting thatthis very low bias current operation of the input transistors in FIG. 3provides excellent DC characteristics but degrades the high frequencyperformance of these devices. Thus not requiring good AC performance theDC operation can be optimized, whereas with the circuit of FIG. 1 theconflicting requirements between AC and DC performance force acompromised design, when the circuit is used as the control amplifier.

The DC reference shifting circuit in FIG. 3 includes a pair ofemitter-coupled transistors 32 and 34 connected to a current sink 45 andfurther connected in a Darlington type connection to transistors 36 and38. A single output transistor 43 is used for current gain and isconnected to the collectors of transistors 34 and 38. A resistive biasnetwork, including resistors 39 and 41, is connected between the outputterminal 29 and ground potential and provides a feedback signal totransistor 38. The output voltage at terminal 29 is sampled and comparedwith a reference voltage V at the input transistor 36, and the currentflow into transistor 43 is controlled in accordance with the comparisonof these two voltages to thereby maintain a constant regulated DCreference voltage at the output terminal 29. This reference voltage isused as the DC reference voltage at the base of transistor 20 in FIG. 2.Thus, the reference voltage applied to transistor 20 is a temperaturestabilized reference voltage equal in magnitude to the desired outputvotlage +V The DC reference shifting circuit in FIG. 3 will be betterunderstood from the following description of the complete monolithicvoltage regulator circuit illustrated in block diagram in FIG. 4 and inschematic diagram in FIG. 5. The circuit in FIG. can be separated intothe various stages shown in FIG. 4 which include a starting andshut-down circuit 47 connected to a bias stage 49. The bias stage 49 isconnected directly to the DC referenceshifting circuit 51 which, inturn, is connected to the control amplifier 53 as previously described.The regulator circuit in FIG. 4 further includes a short circuit currentsampling resistance 59 connected between the control amplifier 53 andthe output load, represented by resistor 55.

Referring now to FIG. 5, the reference numerals used to identify thecontrol amplifier 53 and DC referenceshifting circuit 51 correspond tothe reference numerals in FIGS. 2 and 3 respectively. Other referencenumerals are used to note the additional circuit components in FIG. 5not heretofore described, but some correspondence between referencenumerals in FIGS. 2, 3 and 5 has been maintained to facilitate theunderstanding of these circuits.

The reference voltage V which is applied to the base of the transistor36 in the DC reference shifting circuit 51 is derived from the voltagedeveloped across the Zener diode 43 in the bias stage 49. A firstconstant current source 65 provides a substantially constant currentinto the Zener diode 43 so that the ripple feedthrough from theunregulated input is reduced. The voltage drop across resistor 61establishes the reference voltage for all of the PNP current sourcessimilar to 65, i.e., current sources 65, 67 and 25. This referencevoltage is applied to transistor 44 and, as a result of the offsettingbase-emitter voltages (V 6 of transistors 42 and 44, the voltage at theemitter of transistor 42 is essentially equal to the reference voltageat the base of transistor 44. Therefore, the voltage at the emitter oftransistor 42 is controlled and the resulting current flow throughresistor 59 is independent of variations in temperature.

The transistor 52 in the bias stage 49 serves as a constant current sinkfor the first constant current source 65 previously described and alsofor second and third constant current sources 67 and 25. These threecurrent sources 65, 67 and 25 are connected to a first current sinktransistor 52 via resistors 63, 69 and 71, respectively. The remainingresistive connections to the transistors 58 and 60 and transistors 62and 64 in the current sources 67 and 25, respectively, are identical tothe resistive connections previously described with reference to currentsource 65.

If transistor 42 in the current source 65 has a high current gain(beta), then the collector and emitter currents thereof will besubstantially equal and very little current will flow out of the baselead of transistor 42 into resistor 63. Transistor 44 Will thereforesupply the required current to resistor 63. However, if transistor 42should for some reason have a low beta, then this means that morecurrent will flow out of the base lead of transistor 42 into resistor 63and transistor 44 tends to turn off. Thus, this circuit automaticallycompensates for variations in the current gain of the lateral PNPtransistor 42 which may exist between different fabrication batches ofthe circuit.

The base of transistor 42 is driven from the emitter of transistor 44which has a low value base resistor 61 connected thereto. The resistanceof resistor 61 is effectively reduced by the beta of transistor 44 sothat transistor 42 is essentially being voltage source driven. Thus,with transistor 42 operating in the common base mode, a very high outputimpedance for transistor 42 is provided. Such high output impedance isdesirable because it reduces the effect that any ripple on the inputvoltage applied to the regulator would have on the reference diode 43 orthe differential amplifiers which are biased by the current sources 67and 25.

The bias stage 49 further includes a temperature compensating networkcomprising reference transistor 46, diodes 48 and 50, and resistors 73,and 77. The emitter current of transistor 46 establishes the bias levelsfor the first, second and third current sinks 52, 86 and 92respectively, and the collector current of transistor 46 sets thecurrent levels in the first, second and third current sources 65, 67 and25. Thus, the three current sources 65, 67 and 25 and three currentsinks 52, 86 and 92 are controlled by the biasing of a single NPNreference transistor 46. If reference transistor 46 has a relativelyhigh alpha, which is 0.98 or higher for a high beta, then the emitterand collector currents of transistor 46 will be substantially equal andthe same current will be used to reference all the current sources andall the current sinks in the regulator circuit. This feature insuredexcellent temperature tracking in the circuit. The current flowing inthe above-described bias string, including emitter follower 46, is notdependent upon temperature so that, in

effect, there is a zero temperature coefficient for the current flowingin all of the current sources and sinks.

The bias stage 49 further includes a buffer transistor 57 which isconnected between the current sink transistor 52 and a point 79 in thebias string. This transistor reduces the loading effects on the currentsink transistor 52. Further connected in the bias string 49 is NPNtransistor 54- which interconnects the voltage input terminal 27 to thecollectors of transistors 57, 36 and 32 and is connected at the basethereof to the diode 82 in the DC reference' shifting circuit 51.

The bias stage 49 is so completely independent of the input voltagethat, absent the starting and shut-down control circuit 47, theapplication of an input voltage will not start the regulator by biasingthe Zener diode 43 into conduction. For this reason, a starting andshutdown control circuit 47 is used and includes diode 40, transistor100, Zener diode 41, and resistors 83 and 94. When an input voltage isapplied at terminal 27, current will flow through resistor 83, diode 40and transistor 46. Current source 65 then becomes active and Zener diode43 comes into conduction. When Zener 43 conducts, diode 40 turns off. Asa result of Zener diode 41, which has the same breakdown voltage asZener diode 43, there is no differential voltage across diode 40.Therefore, current will continue to flow through resistor '83 and intoZener diode 41.. If resistor 83 is large, e.g., 60 kilohms, and if thesource of input voltage is in the order of 30 volts, then there will beapproximately 400 microamperes flowing in the starting circuit,resulting in negligible power loss during normal operation of theregulator.

Additional circuitry is included to allow the complete regulator to havea standby or shut-down mode of operation. To enter shut-down, clampingtransistor 100 is brought into conduction by the application of anexternal positive voltage to pin 96 across resistor 94. When shut-down,all current sources and sinks go to zero current and the only bias drainis that current through resistor 83. Thus, the output voltage goes tozero and this feature is desired in some application areas where thiselectronic control would allow seldom needed circuits of a large systemto be in a stand by mode with a substantial savings in powerdissipation. For increased noise immunity in the starting and shut-downcontrol circuit 47, one or more diodes (not shown) may be connectedbetween terminal 96 and transistor 100.

When the external short circuit resistance represented by the externalresistor R samples large currents (=R being very small in the order ofone or two ohms) it will threshold the string of three diodes 97, 98,and 99 and cause the available current from transistor 64 to be bypassed around the Darlington output stage consisting of transistors 24and 26. The output voltage at 29 will therefore fall toward ground.Transistor 45 will detect this reduction in V and will be driven intoconduction. This action will cause the reference voltage at point 35 toalso fall toward ground.

A resistive divider, including external resistors 39 and 68 is connectedin the DC reference shifting circuit 51 between point 35 and ground andis further tied to the base of transistor 38 in the manner describedwith reference to FIGS. 1 and 3. The band-widths of the referenceshifting circuit 51 is reduced by the external capacitor 87 which servesto stabilize the amplifier and reduce the RMS value of the Zener noisewhich is present at the output of the regulator. An additional diode 82is used to isolate capacitor 87 from the circuit in the event of a shortcircuit at the output node 29, and prevent capacitor '87 fromdischarging into and possibly damaging the integrated circuit.

In the monolithic version of the voltage regulator shown in FIG. 5, thepoints 35, 66, 84 and 85 were made external to the die itself and aresometimes referred to as pins. These points or pins may be used tointerconnect external capacitors, resistors and the like. For example,resistors 39 and 68 are connected externally to the die in the circuit(FIG. of the type described which was actually built and successfullytested. However, if desired, these resistors could be formed bydiffusion or other similar techniques using known NPN monolithicsemiconductor processing technology.

Output capacitor 89 is connected directly to the output of the controlamplifier 53. This capacitor is used to stabilize the control amplifierand also to maintain a low output impedance at high frequencies. Thefeedback of circuit 53 is eifective from DC out to some high frequencyat which the circuit begins to lose bandwidth. At such high frequency,the loop transmission cannot respond sufiiciently to prevent the outputimpedance from rising. In order to counteract this increase in outputimpedance at high frequencies, the capacitor 89 is connected across theoutput of stage 53 to hold the output impedance down at highfrequencies. Thus, the capacitor 89 can deliver high frequency currentto the load without the necessity of having the loop active. Therefore,by adding capacitor 89, a dominant pole is created directly at theoutput of the regulator and any increased capacitance at the output 29will improve the stability of the regulator.

Thus, a monolithic voltage regulator circuit has been described whereina control amplifier stage 53 is connected with a feedback loop tieddirectly to the output terminal 29 so that 100% of the output voltage isfed back to transistor 22. This feature insures excellent AC performanceof the regulator. At the same time, a varying DC reference potential isapplied at the input of transistor 20' and this potential is derivedfrom a reference shifting circuit 51 having a resistive feedback looptherein. This circuitry enables the control amplifier portion 53 of thevoltage regulator to be driven by a varying DC reference voltage whichimparts to the overall voltage regulator excellent DC stability.

The following table of values is given by way of illustration only andis not intended to limit the scope of this invention. Such values wereused in a circuit of the type described with reference to FIG. 5 whichhas been actually built and successfully tested.

TABLE Resistors (R) Value (ohms) or fd.)

R39 Depends on V desired external to die 1 3300 R55 Used to simulatecurrent loading of regulator external to die.

R56 514 R59 514 R61 834 R63 1,600 R69 3,200 R71 1,600 R73 4,630 R752,670 R77 700 R78 1,000 R83 60,000 R68 Depends on V desired external todie 7500 R 50 R91 625 R93 416 R94 5,000 R95 1,000 R Depends on maximumload current desired external to die 1 Cin External to die 2 087External to die 0.1 C89 External to die S0 V (volts DC) +3.4 V For R39and R68 as listed (volts DC) +5.0 V (volts min.) {+8.2 (volts max.) 30

1 For Vou'r 0f 5 volts.

I claim:

-1. A series voltage regulator having input and output terminals andoperative to provide a constant DC output voltage in response tovariations in the voltage applied to the input terminal, said regulatorincluding, in combination:

an output control amplifier, said output control amplifier including:

a differential amplifier stage having first and second semiconductordevices differentially coupled to a current sink and operative to bedilferentially switched against each other in response to differentialsignals applied thereto,

said output control amplifier further including an out-put current gainstage connected between said differential amplifier stage and saidoutput terminal for providing a required level of output load current atsaid output terminal,

DC reference shifting means connected to said first semiconductordevice, and comparing a substantially constant reference voltage with afraction of a continuously variable output voltage at said outputterminal to thereby provide continuously variable DC reference potentialfor controlling the conductivity of said first semiconductor device, and

means directly connecting said output terminal to said secondsemiconductor device of said differential amplifier stage to therebyfeed back 100% of the output voltage to said differential amplifierstage and insure both excellent AC and DC performance of said regulator.

2. A series voltage regulator having input and output terminals andoperative to provide a constant DC output voltage in response tovariations in the voltage applied to the input terminal, said regulatorincluding, in combination:

an output control amplifier, said output control amplifier including:

a differential amplifier stage having first and second semiconductordevices therein differentially coupled to a current sink and operativeto be differentially switched and compared against each other inresponse to differential signals applied thereto,

said output control amplifier further including an output current gainstage connected between said differential amplifier stage and saidoutput terminal for providing a required level of output load current atsaid output terminal,

a DC reference shifting circuit connecting a variable DC referencepotential to said first semiconductor device, said DC reference shiftingcircuit having a pair of differentially connected semiconductor devicestherein, one of said pair of semiconductor devices in said DC referenceshifting circuit connected to receive a reference voltage and the otherof said semiconductor devices in said DC reference shifting circuit connected to a resistive feedback loop between the output terminal of saidDC reference shifting circuit and a point of reference potential, saidother semiconductor device comparing a fraction of the output voltage ofsaid DC reference shifting circuit to said reference voltage appliedthereto for providing a varying reference potential at the outputterminal of said DC reference shifting circuit, the output terminal ofsaid DC reference shifting circuit connected to said first semiconductordevice in said differential amplifier stage in said output controlamplifier thereby imparting optimum DC stability to said voltageregulator, and

means directly connecting said output terminal to said secondsemiconductor device of said differential amplifier stage to therebyfeed back 100% of the output voltage to said differential amplifierstage and insure both excellent AC and DC performance of said regulator.

3-. The voltage regulator defined in claim 2 which further includes:

a bias stage having reference transistor therein con ducting a constantreference current and coupled to said DC reference shifting circuit forproviding therein a constant reference voltage which is compared to afraction of the output voltage of said DC reference shifting circuit,

said reference transistor in said bias stage being further connected toa Zener diode which provides a reference potential at said referencetransistor, said Zener diode connected to a source of constant currentand developing thereacross said reference potential which is applied tosaid reference transistor.

4. The voltage regulator circuit defined in claim 3 which furtherincludes:

a starting and shut-down control circuit connected to said bias stage,said starting and shut-down control circuit including a resistor and aforward diode connected in series between said input terminal and saidZener diode and providing a starting current to said referencetransistor in said bias stage when an input voltage is applied to saidinput terminal,

said starting and shut-down control circuit further including anadditional Zener diode connected between said resistor therein and apoint of reference potential, said additional Zener diode becomingconductive after said Zener diode in said bias stage becomes conductiveto thereby decouple the starting portion of the starting and shutdowncontrol circuit from said bias stage.

5. The voltage regular circuit defined in claim 4 wherein said startingand shut-down control circuit further includes a transistor thereinconnected to said Zener diode in said bias stage and operative toreceive an input shutdown control voltage to remove the referencevoltage from said reference transistor and deenergize said voltageregulator.

6. The voltage regulator defined in claim 5 wherein: said bias stageincludes a constant current source feeding a constant reference currentto said Zener diode therein whereby said reference transistor is biasedby a predetermined Zener voltage and conducts a constant referencecurrent, and said reference transistor further connected to a resistivebias string whereby said resistive bias string provides a source ofsubstantially constant reference voltage for said DC reference shiftingcircuit.

7. The voltage regulator circuit defined in claim 6 which furtherincludes:

a second constant current source connected between said input treminaland said DC reference shifting circuit for providing a constant currentthereto, and

a third constant current source connected between said input terminaland said control amplifier for providing a constant current to saidcontrol amplifier.

8. A monolithic series voltage regulator circuit including, incombination:

a control amplifier connected between input and output terminals andoperative to provide current to an eX- ternal load connected to saidoutput terminal, said control amplifier including a differentialamplifier stage thereof having first and second transistorsdifferentially connected to a current sink, said control amplifierfurther including a current gain stage interconnecting said differensaidDC reference shifting circuit connected to said first semiconductordevice and comparing a substantially constant reference voltage with afraction of a continuously variable output voltage to thereby provide acontinuously variable DC reference potential for controlling theconductivity of said first transistor. 9. Avoltage regulator circuitdefined in claim 8 wherein said current gain stage includes first andsecond Darlington connected cascaded transistors interconnecting saidfirst and second transistors in said differential amplifier stage tosaid output terminal, and said first transistor in said differentialamplifier stage connected to said first and second transistors in saidcurrent gain stage for prebiasing said transistors in said current gainstage and insuring that current flows therein as the output load currentapproaches zero. 10. The voltage regulator circuit defined in claim 9which further includes:

a bias stage having a reference transistor connected in a resistive biasstring between said input terminal and a point of reference potential,and a reference diode connected to said reference transistor andproviding a reference voltage thereat so that said reference transistorconducts a substantially constant reference current in' said bias stringand make available therein a reference voltage for biasing said DCreference shifting circuit, said reference voltage is switched againstand compared to a fraction of the output voltage of said DC referenceshifting circuit in a sample and compare type of operation. 11. Thevoltage regulator circuit defined in claim 10 which further includes:

a starting and shutdown control circuit having a resistor a and aforward diode serially connected between said input terminal and saidreference diode in said bias stage for providing a starting current tosaid reference diode upon receipt of an input voltage at the inputterminal, said starting and shutdown control circuit further including aZener diode connected between said forward diode and a point ofreference potential, said Zener diode in said starting and shutdowncontrol circuit becoming conductive and decoupling said starting andshutdown control circuit from said bias stage once said reference diodein said bias stage becomes conductive.

12. The voltage regulator defined in claim 11 which includes:

a first capacitor connected between said second transistor in thedifferential amplifier stage of said control amplifier and a point ofreference potential for providing high frequency currents to loadsconnected to said output terminal and for stabilizing the controlamplifier of said voltage regulator circuit, without degrading thefrequency response of the output impedance of said control amplifier,and

a second capacitor connected between an internal terminal of said DCreference shifting circuit and a point of reference potential to reduceZener noise and to also stabilize said DC reference shifting circuit.

13. The voltage regulator defined in claim 12 wherein said starting andshut-down control circuit further indiode and providing a constantcurrent to said reference diode so that the voltage across saidreference diode does not change with input voltage, said reference diodebeing further connected to said reference transistor for providing aninput voltage thereto so that said reference transistor can establishboth the required reference potentials and a constant temperaturecompensated current in said bias string.

15. The voltage regulator circuit defined in claim 14 which furtherincludes a second constant current source connected between said inputterminal and said DC reference shifting circuit for providing a constantcurrent thereto, and

a third constant current source connected between said first and secondconstant current sources and the differential amplifier'stage of saidcontrol amplifier for providing a'constant current thereto.

16. The voltage regulator circuit defined in claim 15 wherein:

said first, second and third constant current sources each include a PNPtransistor connected to an NPN transistor and have a separate resistorinterconnecting each of said PNP and NPN transistors to said inputterminal so that the emitter of said PNP transistor is essentially atthe same constant voltage as the base of said NPN transistor to therebyestablish a substantially constant current in the resistor connectingsaid PNP transistors-to said input terminal, the reference voltage atthe base of said NPN transistor being derived from the temperaturecompensated current of said bias string via the collector of saidreference transistor, said NPN transistors operating with an additionalcurrent sink which supplies an excess base current for said PNPtransistors, said NPN transistors automatically conducting supplycurrent in addition to the base currents of said PNP transistors toinsure that the current delivered from the collectors of said PNPtransistors is essentially independent of the current gains of said PNPtransistors, the output currents of said PNP transistors beingavailable, respectively, for said reference diode in said bias string,for said DC reference shifting circuit and for said control amplifier,

a first constant current sink referenced to the constant current of saidbias string and further connected to said first, second and thirdconstant current sources for providing constant current paths therefromto allow compensation for variations in current gain of the PNPtransistors,

a second constant current sink connected between the differentialamplifier portion of said DC reference shifting circuit and said pointof reference potential and also connected to said bias string in saidbias stage so that the bias on said second constant current sink iscontrolled by the current in said bias string, and r a third constantcurrent sink connected to said control amplifier and further connectedto said bias string which establishes a bias level on said thirdconstant current sink in accordance with the reference current flowingthrough said reference transistor in said bias string.

References Cited UNITED STATES PATENTS 3,101,442 8/1963 Darbie et al.323-.22 3,122,697 2/1964 Kauders 323--22 3,2Ql,680 8/1965 Ross et al.323-22 X J D MILLER, Primary Examiner A. D. PELLINEN, Assistant ExaminerUS. Cl. X.R. 323-38

